Recently, along with development of information communication societies, the amount of information processing has been increased, and increase in the degree of integration and speed-up of LSIs (Large Scale Integrated circuits) which carry out the signal processing have been required. For the increase in the degree of integration and speed-up of the LSIs, miniaturization thereof is underway; however, along with the miniaturization, loss due to the capacity of an insulating layer between wirings has become a problem, and reducing the permittivity of the insulating layer has become necessary. As the insulating layer, in addition to the reduction in the permittivity, a high mechanical strength is required for processing of the LSIs. Moreover, although resistance of wiring is also reduced by changing the material of the wiring from an aluminum alloy to copper, a thin film such as a barrier film that contacts the wiring is also required to have a function to prevent diffusion of metal, particularly, copper, as well as to reduce the permittivity.
In view of the above-described problems, as the materials of the insulating layer of the next generation, various materials such as a fluorine-containing silicon oxide film (SiOF), a porous silicon oxide film, a fluorine-containing polyimide film, a porous organic coating film, and a SiC-based film have been studied.
However, when an interlayer insulating film is formed of SiOF, the permittivity of the interlayer insulating film is lower than that of conventional ones; however, since the permittivity thereof is about 3.2 to 3.5, reduction of the capacity between wirings, prevention of delay of signals propagation through wiring, and so on have not been sufficiently achieved.
Meanwhile, when an interlayer insulating film is formed of an organic compound material, a permittivity of 2.7 has been achieved by the film in which fluorine atoms are introduced to polyimide or by aryl ether-based polymers; however, it is not sufficient yet. A permittivity of 2.4 can be achieved by a vapor-deposited film of parylene; however, since obtained heat resistance is at most about 200 to 300° C., this restricts the manufacturing processes of semiconductor elements.
Meanwhile, the values of 2.0 to 2.5 have been reported as the permittivity of porous SiO2 films; however, since the porosity thereof is high, there are problems that the mechanical strength (resistance to CMP polishing process) thereof is weak and the diameters of pores are varied.
Furthermore, since these polymer materials and the porous SiO2 films have inferior heat conductivity than conventional SiO2 interlayer insulating films, wiring life deterioration (electro-migration) due to increase in the wiring temperature has been concerned about.
Meanwhile, copper diffuses into these insulating films due to electric fields; therefore, when copper wiring is employed, the surface of copper has to be coated with a diffusion preventing film. Therefore, the upper surface and sidewalls of copper wiring are coated with electrically-conductive barrier metal, and the upper surface is coated with insulating silicon nitride. However, the permittivity of the silicon nitride film is about 7, and the resistance of the barrier metal is much higher than that of copper. As a result, the resistance value of the wiring as a whole increases; therefore, there has been a problem that speed-up of semiconductor devices is restricted.
Meanwhile, when a low-permittivity insulating film is used, a conventional silicon oxide film having good heat conductivity is used in each layer which has connecting holes to connect upper and lower wirings, in order to avoid reliability deterioration. Therefore, wiring capacity is further increased. The increase in the wiring capacity causes signal delay, and there has been a problem that speed-up of semiconductor devices is restricted.
As described above, the aforementioned insulating layer materials are not at levels enough to sufficiently satisfy all of the permittivity reduction, the high mechanical strength, and the function of preventing diffusion of metal, and still have many problems to be solved in a case where the insulating layer materials are applied as an insulating film, for example, low heat resistance and low heat conductivity.    Patent Document 1: Japanese Patent No. 3778164